Iron deficiency affects many infants worldwide and remains a problem among poor and minority infants in the US. Project I uses a systematic, conceptual approach to evaluate the effects of iron deficiency on CNS functions and related behaviors in human infants. The study addresses important unresolved issues. It will determine whether there are effects of iron deficiency without anemia and consider the reversibility of effects following iron therapy. Based on previous findings in iron deficiency, the assessments will target CNS processes of myelination and neurotransmission and particular brain regions (hippocampus and basal ganglia). We will use behavioral and neurophysiologic measures that are sensitive and have evidence for their neural correlates. This approach will be a major advance over the general reliance on global measures in previous studies. 135 healthy 6-month-old infants from an economically stressed Latino community in southwest Detroit will be enrolled: 35 with iron-deficiency anemia, 50 with iron deficiency but no anemia, and 50 non-anemic controls with good iron status. Enrollment will entail screening an estimated 1750 babies. The brain/behavior assessment has 4 components: visual (VEPs, visual acuity, eye blink); neurocognitive (recognition memory, reaction, spatial working memory, attention); motor (reach and grasp, spontaneous motor activity, overall motor development); and affective/neuroendocrine. The infants will be reevaluated after 3 and 6 months of oral iron therapy. To help validate the primate model, infant measures are comparable, insofar as possible, to those in Projects II and III (monkey infant studies). Explicit conceptual and behavioral links to Project IV (developing rodent) make it reasonable that the cellular-molecular, mechanistic studies of that project will inform interpretation of results in this study of human infants. Thus, the proposed project represents a significant step forward in addressing unresolved questions about iron deficiency, the most common single nutrient disorder in the world.